At that point, "Oh, sorry, I was just about to call you. We'll have to do the BBQ another day." OR "Okay, but I didn't buy enough to grill for that many people. Someone else will have to pick up some more food."

Scumbag Steve/Stacey implies that the person the meme is about is rude and inconsiderate and will often do things either actively against or something extremely inconvenient for another person, usually the person making the meme. In this case the OP invited two people over for a good time and those people invited seven eight more people without OP's knowledge or permission, which is a very douchey thing to do